docs: def ToSTMag(self, wave, flux, **kwargs):
          """Convert to ``stmag``.
  
          .. math::
  
              \\textnormal{ST}_{\\lambda} = -2.5 \\; \\log(\\frac{hc}{\\lambda} \\; \\textnormal{photlam}) - 21.1
  
          where :math:`h` and :math:`c` are as defined in
          :ref:`pysynphot-constants`.
  
          Parameters
          ----------
          wave, flux : number or array_like
              Wavelength and flux values to be used for conversion.
  
          kwargs : dict
              Extra keywords (not used).
  
          Returns
          -------
          result : number or array_like
              Converted values.
  
          """
          arg = H * C * flux / wave
          return -1.085736 * N.log(arg) + STZERO